Every time a car brakes, energy
is generated. At present this energy is not used, but new research shows that
it is possible to save it for later use in the form of compressed air. It can
then provide extra power to the engine when the car is started and save fuel by
avoiding idle operation when the car is at a standstill.
Air hybrids, or pneumatic hybrids
as they are also known, are not yet in production. Nonetheless, electric cars
and electric hybrid cars already make use of the brake energy, to power a
generator that charges the batteries. However, according to Per Tunestål, a
researcher in Combustion Engines at Lund
Univ. in Sweden, air hybrids would be much
cheaper to manufacture. The step to commercialization does not have to be a
large one.
“The technology is fully
realistic. I was recently contacted by a vehicle manufacturer in India which
wanted to start making air hybrids”, he says.
The technology is particularly
attractive for jerky and slow driving, for example for buses in urban traffic.
“My simulations show that buses
in cities could reduce their fuel consumption by 60%”, says Sasa Trajkovic, a
doctoral student in Combustion Engines at Lund University
who recently defended a thesis on the subject.
Sasa Trajkovic also calculated
that 48% of the brake energy, which is compressed and saved in a small air tank
connected to the engine, could be reused later. This means that the degree of
reuse for air hybrids could match that of today’s electric hybrids. The engine
does not require any expensive materials and is therefore cheap to manufacture.
What is more, it takes up much less space than an electric hybrid engine. The
method works with petrol, natural gas, and diesel.
For this research the Lund researchers have
worked with the Swedish company Cargine, which supplies valve control systems.
The idea of air hybrids was
initially hit upon by Ford in the 1990s, but the American car company quickly
shelved the plans because it lacked the necessary technology to move forward
with the project. Today, research on air hybrids is conducted at ETH in Switzerland, Orléans in France, and Lund
Univ. in Sweden. One company that intends to
invest in engines with air hybrid technology is the American Scuderi. However,
their only results so far have been from simulations, not from experiments.
“This is the first time anyone
has done experiments in an actual engine. The research so far has only been
theoretical. In addition, we have used data that means we get credible driving
cycle results, for example data from the driving patterns of buses in New
York”, says Sasa Trajkovic.
The researchers in Lund hope that the next
step will be to convert their research results from a single cylinder to a
complete, multi-cylinder engine. They would thus be able to move the concept
one step closer to a real vehicle.